Modulated wave amplifier



Patented May l2, 1942 Farc lMoDULa'rEn WAVE AMPLIFIER Henri Chirex andJacques Fagot, Paris, France,

asslgnors to Compagnie Generale de Telegraphic Sans Fil, a corporationof France Application November 22,1939, serial No. 305,580

In France December 29, 1938 4 Claims.

In Fagots United States application #307,022 filed December 1, 1939, hasbeen disclosed a modulated wave amplifier system with a high efficiencypower stage wherein means is provided to improve the linearity of theamplification system. In the said system the amplifier comprises a twotube stage the tube inputs of which are excited by out-of-phaseamplitude modulated waves. The outputs of the tubes are combined andmeans is provided for altering the phase displacement of the combinedvoltage when the overall characteristic is non-linear to thereby modifythe resultant of the combined voltages to insure linearity.

Our present application discloses in detail and with precision improvedmeans to be used in such a system where a large power transmitter isdealt with, theiinal amplifier of which comprises two stages each havingat least a pair of tubes in symmetric circuits and therefore comprisingat least four tubes in the output end or multiples of four tubes. Itwill be an easy matter for the man trained in the art, by omittingcertain elements, to adapt our circuit organization to the use of onlytwo tubes, i. e., two single tube stages, thus resulting in and forminga simple or plain arrangement.

It has been pointed out in the said prior application referred to abovethat the amplification system or method therein disclosed resembles insome respects the so-called phase-shift modulation or the Chireix systemvof outphasing modulation. The underlying theory of the Chireix systemhas been set forth especially in Proceedings of the Institute of RadioEngineers, November 1935.

In the Chireix phase shift amplitude modulator the load is coupled to awave source over two separate paths wherein the waves are displacedrelatively in phase, each path includingr a phase modulator the twomodulators being operated differentially so that the two paths suppliedto the load two components the phase .relation between which ismodulated continuously in accordance with modulating potentials toproduce a resultant the amplitude of which as a consequence varies inaccordance with said modulating potentials. Systems of this generalnature have become known in the art as outphase modulation systems.

In the system disclosed herein and in said prior application we have anamplifier system which in some respects in some parts of its operationresembles,l the said Ch`ireix system. We supply cited by three voltagestwo of which are opposed in relation and a third of which is`out ofphase with respect to the first two, time being, that the two opposedvoltages are about equal and`cancel so that the third voltages ofvarying amplitude excites the tubes. The tubes as excited provide anoutput comprising phase displaced components which combine to produce aresultant the amplitude of which depends on the -amplitude of thecomponents. In this manner, the modulation is repeated. The operation asdescribed above takes` place for outputs equal to and less than carrieroutput; that is, for outputs below which saturation in the load is notinvolved. However, as the output grows, above carrier output, saturationmay take place in the load. To prevent this, one of the opposed voltagesis caused to represent the output voltages and when saturation takesplace this voltage no longer grows linearly with respect to theexcitation voltage so that the phaserelation between the two outputcomponents changes; that is, the phase displacement changes bringing the-phases closer together and the resultant increases to counteract theeffects of saturation.

Briefly, in our system, the two output components are in fixed phaserelation and variable amplitude for outputs below the amplitude at whichsaturation occurs and are of varying phase and varying amplitude foroutputs of carrier amplitude and greater. The object of our presentapplication is to provide a new and improved circuit arrangement in asystem broadly as described in the prior application.

Our end or power amplification circuit is in a preferred embodimentofthe system in application #307,022. The essential difference inoperation between our system and the said Chireix system resides in thefact that for all states of an instantaneous power below carrier power,the sys- In describing our invention, reference will be modulated waveenergy to a load by tubes eil-'55 made to the attached drawing whereinFig. 2

Assume, for the modulation cycle.

illrstrates a modulated wave amplifier arranged in accordance with ourinvention;

Fig. 'illustrates means for deriving certain of the voltages used inFig. 2; while Fil. 1 illustrates the operation of certain elements ofthe system of Fig. 2 to provide voltages used in Fig. 2.

By reference to Figures 2 and 3, there shall now be described in a briefand summary form, the

regulations as well as the mode of operation.

In Figure 3, T designates a transmitter delivering modulated radiofrequency wave energy into a tuned circuit comprising a capacity and aninductance I, I', I", this energy being absorbed in thtuned circuits 2,2', 2", shown in Figure 3 and, more completely, in Figure 2. The tunedcircuits 2 and 2' loaded bly resistance R represent the circuits whichexcite the grids g and g' of each of the tubes connected in a symmetricmanner, while the tuned circuits 3- and 3' constitute output circuits ofthese same tubes. It is to be noted parenthetically that what is heremeantby tuned circuits is that if the connection at the points m and niscut, the load of the tubes becomes purely ohmi'c in nature. Thecondensers N are neutrodyne condensers,l while 4 and I denote blockingcondensers and blocking inductances respectively of the usual type. `Theoutput circuits 3 and 3 are respectively coupled with the antenna,represented schematically by the resistance R, by magnetic couplingmeans, comprising inductance 6, and an electrostatic couplingmeans,'comprising the condenser I0. These elements 6 and Il!) constituteanother tuned circuit. The magnetic coupling is made equal to theelectrostatic coupling. In these circumstances, theory demonstrates thatthe potential U (see vector adjacent 2 and 2') across the terminals of Ris in phase with the symmetric excitation S and that, if the couplingimpedance, z, of inductance Ii or condenser I0 is united with the loadresistance R by the relation the tubes will still work upon a pureresistance when the interruptions at points m and n are re-closed andthat the excitations across the two circuits 2 and 2. instead of beingin phase, are

shifted in their phase relations an angle 2l); in`

the sense of a leading shift towards the lefthand side and a lag towardsthe right. system disclosed here and in the above mentioned UnitedStatesV application the said (angle 01) relation will occur when energyof carrier wave -amplitude is handled and the said angle will stay xeclfor all lower instantaneousl outputs. This angle, however, will grow forall instantaneous states of larger` power, whereas in Chireixs outphasemodulation the phase modulation angle 0 i. e., the angle of combinationof the phase modulated components, varies throughout the entire Forinstantaneous outputs larger than carrier output, the output circuit ofthe tubes thus is no longer very sharply tuned, though the power factorwill stay high as soon as 0i is of an order ranging between 20 to 25degrees or over.

If the circuit organization is limited to what has been outlined, itwill be an easy matter to see that with the excitations at 2 and2',being in phase the current flowing in load R would be oi' zero value,regardlessof how large these supposedly equal excitations may be. (Thiswould In the V=\/(E-U)2+S2 in such a way that at the carrier waveworking state, the alternating potential set up at 3 and 3 balances thedirect-current potential (small loss potential) then satisfactoryemciency and out put of the last stage in the presence of the saidworking state will be realized (tuned circuit and low loss potential).

For lower instantaneous powers, with the system being linear, the anglesof the excitations at 2 and 2 remain fixed andthe output will beproportional to the instantaneous amplitude. powers above the carrierstate, and because of the saturationof the alternating potential arisingin 3 and 3', U will tend to stay stable, that is will not increaselinearly with respect to the -original excitation voltage say S and theangle 0 will grow resulting thus, in a growth of U. A

straight-line condition or linearity will be ap-l proached so much moreclosely, the greater E-U/E compared with unity.

What remains to be explained is how to obtainin an easy and ready waythe said potentials E and U. For this purpose, reference shall be madeto Fig. l'. Assume E and U are two sources of like phase and of unequalamplitude, and that E is greater than U. If LC is a tuned circuit and Awand l/vw are two equal and opposite reactances, that is to say, ifxw=1/yw=Zo, we have the equivalent of a double or twin circuitorganization of constant intensity. Denoting by E-U the potential acrossthe terminals of R there results:

E-U=-j(E-U) .B/Zo

irrespective of what may be the values of E and of U. This, therefore,furnishes a simple means to'secure the desired quadrature relationshipsbetween E kor U and S. Moreover, calculation shows that E and U workupon a pure resistance.

If E and U each operate upon two arrangements like the one shown in Fig.1, the first one for E beginning with a series inductance A and thesecond one also for E with a capacity 'yw two tuned circuits would haveto be connected in shunt relation to E and U. The embodiment of Fig. 2already has the required circuits. Circuit 2" excited by the transmitterand tuned vis connected with terminals A and B of part of the circuit 2,and with terminals A'B' of anoth'er part of the circuit 2' by thecondensers and inductances x and fy.

Moreover, the outgoing feeder brought to the tuned antenna is connectedin the same fashion with points A, A', B, B'. It will be noticed that besimilar to Chireixs system at minimum out- 7s Itl will also be noticedfinally tha-.tall of the For circuitshere indicated are strictly andsharply in tune for this promotes and facilitates the regulations.

In the arrangement disclosed in Fig. 2 then voltages represented by thevectors S are supplied to each of the tubes in each stage say forexample the tubes in the le'ft hand stage from circuit 2. Voltagesrepresented by the vectors E are also supplied to the grids of each ofthe said tubes from transformer and the circuits connecting the same topoints A and B. The rej ing input and output electrodes, means forapsistance R and its associated antenna supplies antenna voltages U inquadrature to voltages S and in phase opposition to voltages E to thegrids of the said tubes. Voltages E and U buck. The output components ofthe two tubes are displaced in phase so that they combine to produce aresultant which corresponds to the amplitude variations of therespective components.

As pointed out in detail hereinbefore for outputs less than saturationoutput, the phase relation of the output components stays fixed.However, for amplitudes which cause saturation the component U does notincrease linearly with the excitation voltage and as a consequence thevectors U do not increase linearity, E is not fully opposed and phasedisplacement takes place. This phase displacement results in adecreasing of the phase displacement between the output components ofthe two tubes and as a consequence increases the combined resultant tocorrect the.

non-linearity. The stage at the right hand side operates in a likemanner to produce a resultant in phase with the resultant mentionedabove.

What is claimed is: 1. In a modulated carrier wave amplifier, a loadcircuit, a source of modulated wave energy, pairs of electron dischargedevices, each having input and output electrodes, tuned circuit meansfor applying voltages from said source substantially in 'phaseopposition on the input electrodes of the devices of said pairs, othermeans for applying voltage from said source substantially in phaseopposition on the inputvelectrodes of the devices of said pairs ofdevices, said last named voltagesas applied being displaced in phaserelative to the second named voltages applied to said devices, a

load connected with said output electrodes, and

additional means for impressing voltages from said load substantially inphase opposition on the .input electrodes of the devices of said pairsof devices, said last voltages as applied also being in phase oppositionwith respect to said second named voltages as applied to the inputelectrodes of the devices.

2. In a modulated carrier wave. amplifier, a

plying voltages from said source on the input electrodes of each of saiddvices, other means for applying voltage from said source on the inputelectrodes of said devices, said last'named voltages as applied to theinput electrode of the tubes being displaced in phase relative to theapplied flrstnamed voltages, a load connected with saidoutputelectrodes, and additional means for impressing voltages from said loadon the input electrodes of each pair of said devices, said last voltagesbeing in phase opposition on said input electrode with respect to saidsecond named voltages impressed on the input electrodes.

3. In a modulated carrier wave amplifier, a load circuit, a source ofmodulated wave energy, pairs of electron discharge devices, each havinginput and output electrodes, tuned circuit means for applying voltagesof like phase from said source on the input electrodes of said devices,other means for applying voltage from said source on the inputelectrodes of said devices, said last named voltages being applied tothe input electrodes of the devices in phase displaced relation withrespect to said first named applied voltages, a load connected with saidoutput electrodes, and 'additional means for impressing voltages fromsaid load on said input electrodes, said last voltages also beingimpressed on the input velectrodes of said devices in phase opposition'said source in phase opposition on the input electrodes of the devicesof each pair of devices, said last voltages as applied being displacedin phase with respect to said first applied voltages, a tuned circuitcoupling said load to said output electrodes, and'additional means forimpressing voltages from said load on the input electrodes of thedevices of each of said pairs, said last voltages being impressed inphase opposition with respect to said second named voltages on the inputelectrodes of said devices.

" yHliINl'tI CHIREIX.

JACQUES FAGOT. f

